1. Field of the Invention
The present invention relates to an active-matrix type display apparatus comprising a display substrate, switching semiconductor elements formed in the substrate, and memory elements formed in the substrate, for storing signals. More particularly, it relates to an active-matrix type display apparatus whose signal lines are driven by an improved method.
2. Description of the Related Art
An active-matrix type liquid-crystal display is attracting attention. It is regarded as a display which can be modified into a flat-panel display or a high-definition projection TV screen, which displays high-quality images comparable with those displayed by a cathode-ray tube (CRT). A liquid-crystal display of this type comprises a display substrate, pixels formed on the substrate, signal lines for setting the pixels at specified potentials, gate lines, signal lines for selecting the pixels to be energized, a signal-line drive circuit for driving the signal lines, and a gate-line drive circuit for driving the gate lines.
Both drive circuits are integrated circuits (ICs). The signal-line drive IC which is operated by an intermediate-voltage power supply, e.g., a power-supply system of 12V or more, in consideration of the voltage applied to the liquid crystal and the method used to drive the signal lines and the gate lines. This is because, although it suffices to apply a voltage of 5V (absolute value) to the liquid crystal, the signal lines need to be driven at 2 to 12V (7V.+-.5V), while setting the common electrode at 7V, for example, in order to drive the liquid crystal with an AC current.
In recent years it is demanded that the drive frequency be increased to achieve high-definition dislay by using a great number of pixels, the signal-line drive IC and the liquid-crystal panel be made at low cost, and the singal-line drive IC be one which can be driven by a 5V power-supply system and thus can be made small. Proposed as a method in which a 5V-drive IC is drive signal lines is the so-called "common inversion drive." In this method, the voltage applied to the common electrode is altered, repeatedly, each time in accordance with the polarity of the voltage applied to the liquid crystal.
In order to accomplish high-definition display, it is desirable that each signal line and one pixel electrode be spaced apart as little as possible. However, the shorter the distance between the signal line and the pixel electrode, the greater the capacitance crosstalk between them. If the crosstalk is too large, there will be a luminance difference between the upper and lower parts of the display screen, inevitably degrading the quality of the image displayed. To prevent the image-quality degradation, it is proposed that the 5V -drive IC drive the signal lines in another method generally known as "signal-line inversion drive," in which any two adjacent signal lines are set at opposite polarities, thereby to prevent the image-quality degradation.
The common inversion drive method cannot be performed along with the signal-line inversion drive method in which any two adjacent signal lines are set at opposite polarities. Consequently, it is difficult to use a 5V-drive IC, which has a low withstand voltage, in order to display high-quality images. Thus it is difficult to reduce the power-supply voltage for the drive IC and to prevent an image-quality degradation which may results from the capacitance crosstalk between each signal line.and any pixel electrode.